The spring Daylight Saving Time change in the United States begins on the 2nd Sunday in March. This year, that date is Sunday, March 8, 2015 at 2 am. Therefore, Americans in most of the 50 states should prepare spring forward, setting their clocks forward one hour at 2 am on Sunday, March 8, 2015

For the answer to a different form of the question -- when did Daylight Saving Time begin? -- let's turn to Backstory with the History Guys (Ed Ayers, Brian Balogh, and Peter Onuf). In an episode of the radio program rerun this weekend to coincide with the onset of Daylight Saving Time, they discuss the origins of the concept, by Ben Franklin in Paris:

BRIAN: That’s exactly right. I mean where did daylight savings time come from in the first place? I mean I don’t think it was around back in my time, where we were in perfect synchronicity with the world around us. So why did you guys invent this?

ED: Well, I think we’ve got to throw that to Peter because we know who came up with the idea for daylight savings time.

PETER: Well, it was that visionary Ben Franklin. He was all over daylight savings time.

In 1784, in the Journal of Paris, he was writing about well, the way they kept their time in Paris. And what they did is to sleep all morning because they were up all night. And Franklin did one of these calculations, a characteristic Enlightenment thing. And he’d count the number of candles that had to burn to sustain this misuse of daylight. And it would be an immense savings to the French people.

And they were going into debt at this period, badly into debt. And it led to the French Revolution. So no French Revolution, if they had had daylight savings time.

ED: And they might not have sold Louisiana to us if they wouldn’t had to pay for those candles.

ED: Franklin was the first to admit that he didn’t have the means to implement daylight savings time. So Karin, let’s put it Ed out of his misery. Daylight savings time in the United States started in 1918.

And there’s one thing that consistently in the 20th century got the whole country to go on daylight savings time and that was war. It was actually the Germans who first started daylight savings time in 1916.

BRIAN: So if we were going to fight, then we had to be on the same streets.

ED: Exactly.

PETER: Because you show at a battle and they wouldn’t be there.

ED: Well quite literally, the British did go on daylight savings time, a month later or very shortly after. The real point, Karin, is that Germany, Britain, the United States, go on daylight savings time because we can save energy. It was all about well, where are we spending most of our money on energy? And a lot of it was being spent on lighting when daylight savings time was first introduced and even during World War II.

Then we have this thing called air conditioning that comes along. So that when Richard Nixon, at the height of the energy crisis in the early 1970s, calls for extended daylight savings time, it’s not so clear that we’re really saving that much energy because people have started air conditioning their homes. They come home after work and if they’re in Dallas or Houston or Jacksonville, they turn on the air. And that uses a lot of energy.

When I was younger, Daylight Saving Time began in April and ended in October, so it was about (or a bit less than) half the year. Now it begins in March and ends in November, so Daylight Saving Time actually makes up a greater part of the year than Standard Time. By that standard, so to speak, shouldn't the period of the year now known as Daylight Saving Time be called "Standard Time" and what's now called "Standard Time" be called "Winter Time"?